Volume I 


SEPTEMBER, 1922 


Serial No. 2 


Comparative Psychology 

Monographs 

Edited by 

WALTER S. HUNTER 

The University of Kansas 


with the co-operation of 


H. A. CARR. 

The University of Chicago 

S. J. HOLMES. 

The University of California 


K. S. LASHLEY, 

The University of Minnesota 

R. M. YERKES. 

The National Research Council 


) 


A BEHAVIORISTIC STUDY OF THE 
ACTIVITY OF THE RAT 


BY 

CURT P. RICHTER 

Psychological Laboratory, Phipps Psychiatric Clinic 
The Johns Hopkins Hospital 


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• : 




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QL 73 

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7 


A BEHAVIORISTIC STUDY OF THE ACTIVITY OF THE 

RAT 

CURT P. RICHTER 

Pyschological Laboratory, The Johns Hopkins Hospital 


CONTENTS 

Introduction. 1 

I. Periodic nature of spontaneous activity. 4 

II. Relation of spontaneous activity to food... 8 

III. Relation of spontaneous activity to external temperature. 16 

IV. Relation of spontaneous activity to illumination. 20 

V. Relation of activity to age... 24 

VI. Persistence of rhythms of activity after withdrawal of rhythmic 

stimulus.• 31 

VII. On the origin of spontaneous activity. 36 

VIII. Relation of spontaneous activity to hunger. 48 

References. 54 


INTRODUCTION 

Interest in human psychology is moving rapidly toward prob¬ 
lems of general adaptation involving responses of the whole 
organism in actual working life-situations. This change of 
interest is due probably in large part to the healthy impetus 
given to psychological research by recent work and discoveries in 
the allied field of psychiatry. But, undoubtedly, it is also due 
to the strong influences from biology, especially that part of 
biology which is spoken of as behavior. 

This change of interest is probably more radical than it appears 
at first glance. It really represents an entirely different approach 
to things. The older psychology began with the study of the 
function of parts of the organisms, isolated responses (witness 
the work on sensations and memory) and then attempted to put 
these parts together. The error was made in neglecting the fact 
that the integration of parts often produces something—a novelty 
(Holt)—which could never be predicted from the study of the 













2 


CURT P. RICHTER 


function of the parts alone. This older psychology was further 
characterized by a complete unwillingness to see the biological 
aspects of the organism’s reactions, the place of the reactions in 
the life situations. 

The trend of present day psychology stands in marked contrast 
to this older view. The tendency is now to begin with the study 
of the responses of the total organism—intact—and in the situa¬ 
tion in which it ordinarily finds itself. Here the biological as¬ 
pects of the problems stand decidedly to the fore as is evidenced 
by the general current usage of such terms as adaptation, responses, 
reactions, adjustments. It is the behavior of the organism that 
is of most interest, what the organism does , and how it works. 

By what the organism does, is meant simply the description of 
all of the operations and activities involved in the adjustment of 
the organism to its environment. This would include the de¬ 
scription of the objects in the environment responded to, the 
nature and kind of responses made to these objects, the various 
activities elicited by these objects. Further this would include 
also an account of the interrelation of these different activities, 
hunger, sex, social and work activities, for instance, the role 
played by each, the relative importance of each in the life adjust¬ 
ment of the organism. 

The problem of how the organism works deals with the more 
dynamic aspects of behavior. This requires in the first place the 
determination of the origin of the organism’s activity, what it is 
that drives it, so to speak, about in the environment. Further, 
a knowledge of the working of an organism requires a description 
of how the various specific responses are set up as the organism 
is driven about in the environment, how these responses are knit 
together. Here belongs also a knowledge of how the develop¬ 
ment and knitting together of the responses are affected by such 
factors as early frights, shocks, trauma, distortions and limita¬ 
tions of activities. 

At present these problems can not easily be attacked in humans 
for obvious reasons, despite the fact that many abnormal patients 
may be considered as Adolf Meyer so interestingly suggests, as 
“ experiments of nature. ” In most humans the early determin- 




BEHAVIORISTIC STUDY OF THE RAT 


3 


ing factors are rarely definitely known and controlled. Because 
of these difficulties recourse must be had for the present to study 
of the behavior of animals, where the life situations are after all 
very much less complicated, and where the activities and react¬ 
ions may be changed and distorted at will under controlled 
conditions. 

It is largely for the solution of problems of this nature that 
animal psychology must be looked to for help in the future. 
Work in this field is at present at a very low ebb, chiefly for the 
reason that investigators have limited their interests almost 
completely to the study of the part reactions of animals (reac¬ 
tions to lights, colors, sounds, learning problems) and have en¬ 
tirely neglected the broader biological aspects of the lives of 
animals. 

The work presented in the following pages represents an 
attempt to attack these problems from the angle of the life and 
responses of the whole organism. The attack is made on the 
most easily approachable and least difficult points. It includes 
only a small part of the total behavior problem, the study of gross 
bodily activity before it has become specifically connected with 
any of the many complicated features of the environment. The 
relation of this activity to certain vital factors of the environ¬ 
ment, food, temperature, illumination is first examined. This is 
followed by an examination of the origin of the activity, what it 
is that causes the animal's activity. Finally the relation of this 
diffuse undirected activity to one of the animal’s most important 
specific responses, its food-seeking activity (hunger reaction), 
is examined. 

In making this study of the gross bodily activity of the rat the 
emphasis is laid throughout on what the animals do of their own 
accord, free from all external stimulation. For after all, there is 
a marked difference however not well recognized, between what 
an organism can be made to do and what it does of its own account 
(internal stimuli). The emphasis is usually placed on the former, 
that is on the training element—this is true particularly in the 
whole field of education probably even more so than in the field 
of animal psychology. Interest has only recently begun to 


4 


CURT P. RICHTER 


be directed toward the spontaneous activities of humans and 
animals. 

The present work was carried on in the Psychological Labora¬ 
tory of the Johns Hopkins University under the direction of Dr. 
John B. Watson. I am deeply indebted to Dr. Watson for his 
help and encouragement and for the complete freedom allowed 
me in carrying on my work. The inspiration to this work came to 
a very great extent from the numerous suggestive experiments of 
Cannon and Carlson on the Hunger Problem. It came also from 
the Behavior work of Jennings on the Lower Organisms and from 
the many stimulating experiments of Szymanski on Activity 
Problems. I am very much indebted to all of these workers. I 
am indebted for help and criticism to Dr. Edwin B. Holt, Dr. 
Knight Dunlap, Dr. H. H. Donaldson, and Dr. E. Sanford. I am 
also indebted to my friends Mr. Ging Wang and Mr. David 
Brunswick for many helpful suggestions and assistance. 

I. PERIODIC NATURE OF SPONTANEOUS ACTIVITY 

For carrying out the purposes of the following experiments two 
things were required: (1) A situation as free as possible from all 
active external stimulation, and (2) an arrangement for recording 
the activity of animals over long periods of time without in any 
way stimulating the animals themselves. 

The conditions of the first requirement were met in the following 
way. Noises were eliminated by carrying on the experiments in 
a room fitted with large double sound-proof doors and very 
thick sound-proof walls. All avoidable odours were taken care 
of by a very good ventilation system. The air was always 
fresh and free from the usual odors found in animal laboratories. 
The room was made completely impervious to light rays from 
the outside by placing heavy covering of cloth and many layers 
of thick opaque paper over the window. Because of the double 
doors and thick wall the room was also almost completely im¬ 
pervious to temperature changes from the outside. It was 
possible to maintain the temperature at one constant level for 
weeks at a time. The conditions of the second requirement were 


BEHAVIORISTIC STUDY OF THE RAT 


5 


met by means of the construction of small triangular shaped wire 
cages large enough to permit the animals to move about freely. 
A photograph of one of these cages is shown in figure 1. This 
cage is 10 inches high and each side is 14 inches long. It has an 
aluminum bottom fastened to the cage. The bottom is sup¬ 
ported under each corner on a rubber membrane stretched 
tightly over a large tambour. The tambours are connected 
together immediately under the cage into one tube which is led to 
a small Marey tambour, the lever of which records on the smoked 



Fig. 1. Activity Cage 

paper of a kymograph. By this means every movement of the 
animal, even the slightest, is recorded on the drum with a single 
mark. The cage and support are rigid enough to prevent any 
stimulation arising from shaking of the cage or from insecurity 
of foot-hold. 

The attack on this problem of the spontaneous gross bodily 
activity of the rat was begun with the simple experiment of 
observing what happens to the activity when the animals are 
placed in a situation described above free from all external 
stimulation in constant complete darkness. A typical record 







6 


CURT P. RICHTER 



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obtained from an animal under these con¬ 
ditions is shown in figure 2. It is seen that 
the rat is alternately active and inactive 
and that the regularity of the recurrence 
of the periods is quite striking. This 
regularity is brought out even better in 
figure 23 on page 50. Frequently when 
the conditions of the experiments are 
particularly well controlled the differences 
in the intervals between the periods does 
not vary more than just a few minutes. 

The rate of the periods was found to 
vary with the age of the animals. In very 
young animals this rate is most rapid, 
averaging about fifteen for the twenty-four 
hours. In old animals the rate averages 
about ten. The length of the activity 
| periods also shows some variation with 
-2 age, being longer in younger animals and 
'2 becoming progressively shorter in older 
.§ animals. 

Szymanski (1) has recently also studied 
the activity of the rat along with the 
activity of many different animals, from 
the simplest insects to the human infant. 
He used an “Aktograph” for his work on 
rats—a device very similar to the activity 
cage described above, except that it is 
supported on springs and registers activity 
directly with a lever rather than pneumat¬ 
ically. Szymanski found that the activity 
of the rat is divided into ten periods per 
• twenty-four hours. What was found in 
the experiment above seems to agree fairly 
well with this result, except that Szymanski 
makes no statement as to the age of the 
animals that he used for his experiments. 
He did not notice the great regularity of 









BEHAVIORISTIC STUDY OF THE RAT 


7 


the recurrence of the periods probably for the reason that he 
made no attempt to keep the conditions of the experiment 
constant over longer periods of time. He did his work in an 
ordinary room subject to the daily changes of temperature and 
illumination due to the day and night on the outside. 

For the reason that the rat shows a number of periods during 
the twenty-four hours Szymanski speaks of it as a polyphasic 
animal in contrast to the monophasic animals, like the human 
adult for instance, which show only one long period of activity 
and one period of inactivity during the twenty-four hours. That 
this classification is of somewhat doubtful value, and that it 
describes their reactions to external stimuli rather than the func¬ 
tion of any mechanism inherent in the organism itself may be 
brought out by the consideration of some experiments on the 



Fig. 3. Record of Spontaneous Activity of Ten Months Human Infant 

During Uninterrupted Sleep 

Time in hours. From work of Miss Tomi Wada 

human infant and adults carried out in the Phipps Clinic Psycho¬ 
logical Laboratory during the past year by Miss Tomi Wada of 
Columbia University (11). 

Miss Wada was able to confirm on humans what was found in 
the experiments on rats. She used the same technique that was 
employed in the rat work. In the human infant she found that the 
same regularity of the alternation of the periods of activity and 
inactivity prevails. She obtained her records chiefly during the 
long period of sleep at night. The frequent interruptions for 
feeding and bathing etc. make it difficult to obtain records of 
activity during the day. A typical curve of the activity of a ten 
months infant during sleep is shown in figure 3. These periods 
come at the rate of one every fifty to fifty-five minutes. The 
regularity of these periods is very striking. Miss Wada found 
further that the activity of the human adult during sleep is also 






8 


CURT P. RICHTER 


periodic. The interval between the periods in the adult is how¬ 
ever considerably longer than in the infant, usually about one and 
one half to two hours. 

Experiments are now being carried on by Mr. Ging Wang in 
the Hopkins Laboratory on the activity of the newly born rat 
before it has had any contacts with the environment, before it has . 
ever nursed, in order to establish whether the periods are present 
at birth or dependent on later environmental influences. The 
results obtained so far seem to indicate that the activity at 
birth is continuous and uninterrupted by regular intervals of 
quiescence. 

The probable relation of these activity periods to certain en¬ 
vironmental influences (the hunger reactions) as well as to the 
rest of the behavior of the organism will be discussed in detail 
in the last two chapters. 

II. RELATION OF SPONTANEOUS ACTIVITY TO FOOD 

It was found at the beginning of this work that the spontaneous 
activity of the rat is very intimately related to the food habits 
of the animal. This relation will now be examined in some detail 
from the following points of view; (1) what happens to spon¬ 
taneous activity (simply the amount of activity, disregarding for 
the moment the periods of activity) when the animal is deprived 
of all food, when it is starved; (2) how spontaneous activity is 
distributed over the day with relation to the last feeding periods 
and also with relation to the time of next feeding (anticipation of 
feeding). 

The general conditions were maintained practically the same as 
above. The laboratory was kept constantly either illuminated 
or darkened over longer periods of time. The temperature was 
kept constant at 23°C. All noises and odors were eliminated. 

The animals were fed punctually at a certain time each day 
(in most of the experiments at twelve noon). Food was placed 
in each cage in specially arranged receptacles and left there for 
twenty-five minutes. Then all of the remaining food was care¬ 
fully removed. This method of feeding gave each animal plenty 
of time to satisfy its hunger under fairly natural conditions. It 


BEHAVIORISTIC STUDY OF THE RAT 


9 


also ensured an accurate control of the amount of food eaten 
from day to day. Actual weighing of the food showed that the 
amount eaten in twenty minutes remains almost constant from 
day to day. The animals developed normally on this method of 
feeding. 1 

For the first part of the experiment eight animals were used. 
Normal activity records were taken for five days preceding the 
beginning of starvation. Four of the animals of this group were 
also deprived of water after the five days in order to obtain addi¬ 
tional information on the relation of activity to water intake. 

The amount of activity per day was obtained by counting the 
marks made on the smoked paper by each movement of the 
animal in the activity cage described above. The kymograph 
was set running just fast enough to enable the marks to be 
recorded individually. 

Three of the animals starved but permitted to have water all 
the time showed a definite increase in activity for the first two 
to three days after the beginning of starvation and then a steady 
marked decrease to a point of almost complete inactivity on the 
eighth day. All of the animals deprived of both food and water 
showed a steady marked decrease in activity immediately. This 
group reached the point of complete inactivity already on the 
fifth day. The results of this experiment are shown in figure 4 
where the days of the experiment are given on the abscissae and 
the total amount of activity per day in activity units (single 

1 In this present work a synthetic diet was used after the formula of Dr. E. V. 
McCollum of the School of Hygiene, Johns Hopkins University. This is an excel¬ 
lent diet. For behavior work on the rat it is ideal. 


Flour (graham). 72.5 

Casein. 10.0 

Milk powder (skimmed). 10.0 

Calcium carbonate. 1.5 

Salt. 1.0 

Butter fat. 5.0 


The importance of using a good diet for all animal behavior work was con¬ 
vincingly demonstrated by the findings of Dr. E. V. McCollum in connection with 
work on feeding problems. He found that the maternal reactions, nest-building, 
caring for young, nursing, are absent in animals fed on poorly balanced diets 
especially diets low in proteins. These animals often eat their young. 








10 


CURT P. RICHTER 




Fig. 5. Ratios of Total Amount of Activity During First and Second 
Twelve Hour Periods Following Single Daily Meal 







































BEHAVIORISTIC STUDY OF THE RAT 


11 


marks on the kymograph paper) on the ordinates. The average 
daily activity for the five days preceding the experiment is given 
on the first ordinate. 

In the next experiment on the distribution of activity with 
relation to the time of feeding it was first undertaken to determine 
simply how the amount of activity of the first half of the day 
(the first twelve hours after the feeding period) compares with 
the activity during the second half. It was found that the activity 
during the first twelve hours is very much greater than during 
the second twelve. But the ratio of the amount of activity 
during the first twelve hours to the activity during the second 
was found to depend on the age of the animal. This is shown in 
figure 5 where the age in days is given on the abscissae and the 
ratio of the amount of activity during the first and second halves 
of the day are given on the ordinates. It is seen that the very 
young animals are almost twice as active during the twelve hours 
immediately following the daily meal than during the next twelve. 
In the very old animals the amount of activity during these two 
periods is almost evened out. This curve is based on records 
from thirty-five animals of three different ages. 

When instead of dividing the twenty-four hours following the 
time of feeding into two twelve-hour periods they are divided into 
one hour periods, the curve of the distribution of activity has a 
very characteristic form. Such a curve is shown in figure 6. 
This curve is based on the records obtained from forty animals 
250 days old. In this figure the time of the day is indicated on 
the abscissae in hours, while the amount of activity per hour is 
indicated on the ordinates. The animals were fed at 12 o’clock 
noon. The room was kept in constant illumination. It is seen 
that immediately following the daily feeding period there is a 
period of relative inactivity lasting from four to five hours. Then 
there follows a period of very intense activity for eight to ten 
hours. This is followed in turn by a period, lasting from five to 
seven hours, of almost complete inactivity. During the last 
two to three hours of the twenty-four the activity increases very 
rapidly again right up to the time of the next feeding period. 


12 


CURT P. RICHTER 


In order to avoid misunderstanding it may be well to emphasize 
here that this curve is a composite curve made up of the individual 
curves of forty animals. The individual curves of course look rath¬ 
er different. A typical individual curve is shown in figures 17 and 
18 on pages 33 and 34. In these curves the alternation of periods 
of activity and inactivity stands out very clearly. These periods give 
the curves a very ragged and irregular outline. The general form of 
these curves corresponds however to that of the composite curve 
shown in figure 6. During the inactive parts of the curve the 
amount of activity in each activity period is relatively very small 
but the periods are present nevertheless. The discrepancy 
between Szymanski’s results and the results presented in the 
previous chapter on the number of activity periods per day may 
be due to the fact that Szymanski failed to take these small 
periods into account. The importance of these small periods will 
be brought out in another place. 

The activity distribution curve shown in figure 6 was for 
animals 250 days old. The form of this curve becomes very 
much modified in very young animals and as well in very old 
animals. In the former the “hump” of activity begins almost 
immediately after the daily feeding period, figure 7, while in the 
latter its onset is very much delayed. The “hump” of activity 
is most striking in animals about 200 days old. After that age it 
becomes less and less marked until in old age, over two years, 
the curve becomes smoothed out and the hump is obliterated. 
This is shown schematically in figure 8. 

In order to make certain that the shape of the activity dis¬ 
tribution curve shown in figure 6 did not depend on any external 
factors, for instance very slight changes of illumination imper¬ 
ceptible to the human eye due to the daily change of light and 
darkness on the outside of the laboratory, or else that the curve 
did not depend on the general city noises and sounds of the day, 
the time of feeding was changed from 12 o’clock noon to 12 o’clock 
midnight, also to 8 o’clock in the evening. In all cases the shape 
of the curve remained practically the same. This was true also 
when records were taken during constant illumination which 
seems rather conclusive evidence against changes in illumination 
having anything to do with results obtained. 



Twenty-four Hours with Relation to Time of Feeding 


Time is given on the abscissae in hours. The amount of activity during each 
hour is given on the ordinates. For animal 250 days old. 







14 


CURT P. RICHTER 


These experiments show that the rat is naturally inactive for 
a time after eating, and that it does not become active again of 
its own accord for several hours afterwards. These results bear 
out essentially the observations man has made on his own be¬ 
havior, for there is a general saying that it is not a good thing to 



Fig. 7. Curve Showing Distribution of Spontaneous Activity with Rela¬ 
tion to Time of Feeding 

For animals about forty days old 






BEHAVIORISTIC STUDY OF THE RAT 


15 





Fig. 8. Schematic Curves for Different Aged Animals Showing How Spon¬ 
taneous Activity is Distributed Over the Twenty-four Hours 
with Relation to the Time of the Single Daily Feeding 















16 


CURT P. RICHTER 


work directly after eating. Sayings of this nature are fre¬ 
quently apt to be colored by fictions and superstitions, but this 
one seems to be based on fact. If the same curve holds for man 
that holds for the rat it would then seem advisable for man when 
he has work to do, to do it during the period of maximum spon¬ 
taneous activity, that is when the body cooperates, rather than 
during the period of natural inactivity when the body does not 
cooperate. 

III. RELATION OF SPONTANEOUS ACTIVITY TO EXTERNAL TEM¬ 
PERATURE 

Temperature and illumination are factors which are present 
in the environment of all organisms at all times and which can 
never be eliminated. They are vital factors. They are present 
in all situations from the simplest to the most complex, so that a 
thorough knowledge of their relation to activity is of prime im¬ 
portance for the solution of any kind of behavior problems. 

The difficulties of studying the relation of behavior to external 
temperature in animals are many. A rather highly specialized 
equipment and technique for obtaining and controlling tem¬ 
peratures at all levels are absolutely essential. Without them 
conclusive results are obtained only with the greatest difficulty. 
In the present work many different temperature experiments were 
tried, but with the exception of one or two all of them failed to 
give satisfactory results. 

The following experiments deal only with the modifications 
of the normal activity distribution curve, described in the pre¬ 
vious chapter, with relation to external temperatures. The 
conditions of these experiments were essentially the same as for 
the others. The experiments were carried out over long periods 
of constant illumination and constant complete darkness. 
Higher temperatures than the normal 23°C. were obtained by 
means of two electric heaters, while temperatures lower than 
normal were obtained from natural sources during the cold 
months of winter. 

The results of these experiments showed that the characteristic 
shape of the activity distribution curve is very definitely affected 


BEHAVIORISTIC STUDY OF THE RAT 


17 


by changes in external temperature. These modifications affect 
chiefly the position of the period of maximum activity—the 
“hump” in the curve. In a comparatively low temperature 
10° to 15°C. this period of maximum activity begins almost 
immediately after the daily feeding period. The usual interval 
of relative quiescence following the taking of food is absent. 
This may be seen in figure 9. This curve is based on the records 
of four animals of from 200 to 300 days old, taken in an external 
temperature of 12° to 13°C. In a temperature considerably 
higher than the normal 29° to 30°C. on the other hand, the onset 
of the period of activity is very much delayed. The interval of 
quiescence following the taking of food is greatly lengthened and 
the “hump” of activity is not as conspicuous as before. This 
may be seen in figure 10 based on activity records from animals 
of middle age about 300 days in an external temperature of 
29° to 30°C. 

It will be noticed that the form of the activity curve for middle 
aged animals taken in a cold external temperature is very similar 
to the activity curve for very young animals taken at a normal 
temperature. In both cases the period of maximum activity 
begins immediately after the taking of food. Compare figure 8 
and figure 7. Conversely in higher temperature it will be noticed 
that the form of the activity curve of the young animals becomes 
very much like the normal curve for middle aged animals. In 
both cases the period of maximum activity falls near the middle 
of the twenty-four hours. 

The attempt was made to throw some light on quite another 
phase of the relation of activity to external temperature by the 
determination of the external temperature in which an organism 
is most active. In the previous experiments 23°C. was chosen 
quite arbitrarily as the normal temperature. It was found that 
both below (13°C.) and above (30°C.) this temperature the 
amount of activity per day was diminished. Somewhere between 
these two extremes there must be a point at which the animals 
are most active, a “critical” point of activity. It was not pos¬ 
sible to make the determination of this point for the rat for the 
reason that the means at hand of regulating the temperature of 


18 


CURT P. RICHTER 


the laboratory were not sufficient to obtain anything more than 
the very crudest gradations in temperature. 2 



Fig. 9. Distrubution of Spontaneous Activity with Relation to Time of 
Daily Feeding in a Low External Temperature 

Age of animals 200 to 300 days 


2 The attempts that were made to correlate activity with barometric pressure 
and humidity were not successful. It is very difficult to control these factors with¬ 
out an equipment especially adapted to this purpose. 









BEHAVIORISTIC STUDY OF THE RAT 


19 


The determination of this critical point of activity might be 
of help to the physiologist in solving several of the problems of 
animal heat. Work in this field does not seem to have progressed 
very much since the nineties chiefly for the reason that the 



Fig. 10. Distribution of Spontaneous Activity in a High External 

Temperature 

Age of animals about 300 days 





20 


CURT P. RICHTER 


behavior side of the problem—the total reactions of the organisms 
to different temperatures—has been neglected. This may be 
brought out by a consideration of the problem of the relation of 
metabolic processes of the body to external temperature. 
Physiologists speak of a critical point of the temperature of the 
air surrounding an organism at which the metabolism of the 
organism is at a minimum. The increase in metabolism below 
this point is brought about by chemical processes, while the 
increase above this point is brought about either by vaso-motor 
or by respiratory changes, or by muscular or glandular changes. 
Nothing is said however regarding the organism’s activity, its 
total reactions to the changes in temperature. Indeed in most 
of the experiments on this problem the animals are confined and 
tied in very small chambers where not even the slightest movement 
is possible. Without this information of the behavior of total 
activity the physiologist’s study of the problem must remain on 
a purely static level. 

IV. THE RELATION OF SPONTANEOUS ACTIVITY TO ILLUMINATION 

In the environment of all animals and at all times there is 
some degree of illumination or else no illumination at all, that is 
complete darkness. It is of greatest importance in studying be¬ 
havior problems to know just how these ever present factors 
affect the activity of organisms. On the basis of the present 
knowledge on this subject animals are classed as being either 
nocturnal or diurnal, according to whether they are more active 
at night or during the day. This classification as it stands 
at present is based not only on the reactions of the animals to 
the light and darkness of the day and night, but also on the reac¬ 
tions of the animals to other factors of their environment, such 
for instance as possibilities of getting food, attacks from other 
animals, etc. This is a decided limitation. There is still a 
further limitation of this classification, in that it places animals 
in either one group or the other and does not tell just to what 
extent the animals are more active in the dark than in the light, 
or the converse. 


BEHAVIORISTIC STUDY OF THE RAT 


21 


In the present experiments the attempt is made to determine 
whether the rat is nocturnal, and also just to what extent it is 
nocturnal; that is just how much more active it is in the dark 
than in the light. 

This experiment was carried on in the following way. The 
laboratory in which the records were taken was alternately 
illuminated and completely darkened every twelve hours. The 
amount of activity (in activity units) in these two periods was 
measured. Then the ratio of the amount of activity in the dark 
period to the amount in the light period was taken as a numerical 
indication of the active extent to which the animal may be said 
to be nocturnal. 

All conditions were kept the same in both periods, except 
the conditions of giving food. The animals were fed just once per 
day just as was done in all of the previous experiments. Records 
were taken in two series. In one series the animals were fed at 
the beginning of the dark period. In the other they were fed at 
the beginning of the light period. It proved necessary to take 
two series of records in this way because of the fact demonstrated 
in figure 5 above that spontaneous activity is not equally dis¬ 
tributed over the twenty-four hours with relation to the time of 
feeding. There it was shown that the amount of activity in the 
first twelve hours following the daily meal is very much greater 
than during the second twelve hours. Thus in the first series of 
records the effect of the food is added to the effect of the darkness, 
while in the second it is subtracted. Records obtained in this way 
are shown in figure 11. Curve A gives the results in the first 
series in which the animals were fed at the beginning of the dark 
period. The ratios of the amount of activity in the dark period 
to the amount in the light period are given on the ordinates and 
the ages of the animals are given on the abscissae. The ratios 
for animals fed at the beginning of the light period are given in 
Curve B. The great discrepancy between these two curves is 
quite obvious. 

The method by which the effect of food was eliminated may be 
brought out most simply by the following example. It will 
be noticed in the curves A and B in figure 11 that the animals 


22 


CURT P. RICHTER 


3P0 


iso 


loo 


1,50 


too 


0,50 


d 

/v>z 


, 

m 





m 


0 





/fa 

f 

/ J 

?5 


Cy 

m 


Xw 




CfflL 




io 

dALis 


loo 


ZOO ISod Tfod 5&0 too 


Fig. 11. Curves Showing Ratios of Nocturnal to Diurnal Activity at 

Different Ages. 

Figure shows that these animals become more nocturnal with age 















BEHAVIORISTIC STUDY OF THE RAT 


23 


become progressively more active in the dark than in the light 
as they grow older. At 400 days when the animals are fed at 
the beginning of the dark period they are 2.90 times more active 
in the dark than in the light. When fed at the beginning of 
the light period they are only 1.42 times as active in the dark. 
This is shown in a diagram in figure 12. In the first series the 
ratio of the activity in the dark to activity in the light, 2610/900 
is 2.90. In the second series this ratio, 2090/1460, is 1.42. The 
effect of the food was eliminated then by taking the total amount 
of activity in the dark periods in the two series to the total 
amount in the light periods (2610+2090) 4700/(900 + 1460) 
2360 or 1.99. Ratios obtained in this way are shown in curve C 
in figure 11. 


FOOD SERIES a food at beaming of dm period 


LIGHT - 900 


NOON 

Food 


SERIES B 

LIG-H^T ~ i4 6 o 


MIDNIGHT 

FOOD AT BEGIHNW& OF LIGHT PERIOD 


noon 


DARKNESS 2 09 0 


NOON 


MIDN 


WT 


NOON 


Fig. 12 . Diagram Showing How Curves in Figure 11 were Obtained 


This curve shows conclusively that the rat is more active in 
the dark than in the light, in other words that the rat is a noctur¬ 
nal animal. This curve shows further that the rat becomes 
progressively more nocturnal as it grows older. At 60 days it 
is 1.34 times more active in the dark than in the light. From this 
age on this ratio increases rapildy until at 600 days the animal is 
more than twice as active in the dark as in the light. 

Whether or not nocturnal and diurnal tendencies change with 
age in other animals and in man is not definitely known. It is 
generally said that man also becomes more nocturnal in his 
habits with age. There seems to be some truth in this statement 
for it is well known that at birth and for a considerable time 
afterwards the human infant is almost totally inactive in the dark. 















































































































































































24 


CURT P. RICHTER 


Only as he grows older does he begin to stay awake in the dark. 
Gradually he becomes more and more a night animal until in 
ripe old age much of his activity is manifested during the hours 
of twilight or the night. The progressive tendency toward 
nocturnal habits with age in the rat may be explained in a num¬ 
ber of ways, all of them, however, quite unsatisfactory. First, 
as the animals grow older they find that they can forage and climb 
about more freely, with less molestation at night than during the 
day. This would certainly be true in part anyway for animals 
living in the open, but for animals living in the laboratory all the 
time from birth on, it seems quite questionable. Then from the 
point of view of the recapitulation theory, it might be said that 
these results would show that the Albino belongs to a species 
which is in the progress of changing its habitat from places on 
the surface of the earth, trees and bushes, to burrows and holes 
in the dark under the ground. According to this theory as it is 
generally understood the diurnal activity would represent a 
former stage in the life of the rat, just as it is said that the grasp¬ 
ing reflex of the human infant belongs to an earlier stage in the 
development of man. Such theories do not seem to be very 
well-founded. A further possible explanation of the progressive 
change toward nocturnal activity may be sought in the changes 
of the structure of the eye with age, but about this very little is 
known. 

V. RELATION OF ACTIVITY TO AGE 

It was shown in the previous chapters how spontaneous activity 
of the rat is modified by the intake of food, by temperature and 
by illumination. It was brought out incidentally in a number of 
places in these chapters that the expression of activity is also 
dependent on age. This relation between activity and age will 
now be examined in more detail. In the first place a determina¬ 
tion was made of the actual amount of activity at the different 
stages of the animahs life. This necessarily included also a deter¬ 
mination of the age at which the animal is at its maximum of 
spontaneous activity. 


BEHAVIORISTIC STUDY OF THE RAT 


25 


These determinations were made in three different ways: (1) 
On the basis of the spontaneous activity in the simple stationary 
cages, described above. (2) On the basis of the amount of work 
done in the revolving drums, the total number of revolutions made 
at different ages. (3) On the basis of the readiness and com¬ 
pleteness with which nests are built under normal conditions. 

The technique employed in the first method was essentially 
the same as that described in the experiments above. For the 
reason that it was not possible to obtain continuous uninterrupted 
records on a group of rats throughout the entire period of their 
lives records were taken instead at frequent intervals for fifteen 
months on a very large group (40) of animals of all different ages 
(26 to 700 days). Records were taken for five to eight days at 
frequent intervals. In this way a sufficiently large number of 
records were obtained for all stages in the development of the 
rat. Before each series of experiments the animals were given two 
to three days time or longer in which to accustom themselves 
to the cages. Twelve of the animals of the group were left in 
stationary cages all the time in order to eliminate the effects on 
the activity which might be caused by frequent changes back and 
forth from the activity cages to the ordinary cages. The effects 
of these changes on the rest of the group did not prove to be very 
great. Records were taken always under the same conditions 
of temperature and illumination. 

‘ The relation of activity to age determined by this first method 
is shown in figure 14, in the curve marked “Stationary Activity 
Cages. ” In this curve the age of the animals is shown on the 
abscissae in days, while the average amount of activity per day 
in activity units is given on the ordinates in the second column 
labelled “Activity Units/’ In this curve it may be seen that at 
25 days the rat is quite inactive. From this age to the age of its 
maximum activity, 175 days, its activity increases very rapidly. 
After 175 days its activity begins to fall off, slightly at first, then 
fairly rapidly until at 600 days it reaches the original level of 
inactivity from which it started. 

In the second method ordinary revolving drums were used. 
They were 12 inches in diameter and 10 inches wide, and revolved 


26 


CURT P. RICHTER 


very easily as was demonstrated by the fact that 30-gram rats 
were able to turn them as many as 12,000 times in twelve hours. 
A photograph of the drums is shown in figure 13. Six such 
drums were used in this experiment. 

By placing the animals in the drums alternately every six hours 
it was possible to take records on twelve animals at one time. 
Six animals were always running in the cages while the other six 
rested in small separate stationary cages. In this way each 
animal spent twelve out of every twenty-four hours in the drums. 



Fig. 13 . Photograph of Revolving Drum 


The animals used in this experiment were of six different ages, 
30, 100, 210, 250, 450 and 600 days. Records were taken con¬ 
tinuously for one month with the exception of an occasional da} r 
of rest. Only the scores made during the last twelve days of the 
experiment are included in the final record for the reason that all 
of the animals showed very great irregularities during the first 
part of the month while they were adapting themselves to the 
drums. A curve based on data obtained in this way is shown in 
figure 14 in which the age of the animals in days is given on the 
abscissae, and the number of complete revolutions per day are 
given on the ordinates. 






BEHAVIORISTIC STUDY OF THE RAT 


27 



p 100 7@0 3AA " (fahJ ~5d0 boo 100 

Fig. 14. Curves Showing Relation of Activity to Age According to Three Different Methods 










28 


CURT P. RICHTER 


The data from this second method gave the following results. 
In the revolving drums at thirty days the rat is quite active, as 
is demonstrated by the high average at that age of 9000 complete 
revolutions per day. Its activity increases however from this 
age until at 100 days it reaches its maximum. This confirms the 
work of Slonaker (2), who found period of maximum activity lies 
between 81 to 120 days. After 100 days the rat’s activity falls 
off very rapidly so that at 240 days it is already less active than 
it was at thirty days, and at 600 days it is almost completely 
inactive, averaging at this age about 1000 revolutions per day. 

In the third method the relation of activity to age was deter¬ 
mined on the basis of the completeness with which the rat builds 
a nest for itself at different ages under ordinary conditions. For 
this purpose a standard situation was arranged in which the rat 
normally builds itself a nest. A square cardboard frame 3 feet 
wide and 1 foot high was placed on the floor and covered with 
wire cloth. A definite number of small strips of crepe paper 
(200) all of the same size and shape were evenly distributed over 
the floor on the inside of the frame. Four such frames were 
used. A single rat was placed in each frame for a given length 
of time, usually about twelve hours. At the end of this time the 
number of strips of paper gathered into a nest was counted. The 
ratio of this number to the total number available (200) was 
taken as measure of the animars activity. The nests included all 
strips within a radius of four inches of the densest spot. During 
this experiment all external conditions were kept constant. It is 
particularly important to keep the temperature constant for it is 
well known how easily the nest-building activity is changed and 
influenced by changes of temperature. 

In this way the curve marked “Nest-building” in figure 14 
was obtained. The number of strips formed into a nest is given 
in the column headed “Nest-building Units” at the right side of 
the curve. This curve is based on the records for three con¬ 
tinuous days of twelve animals of six different ages. The irregu¬ 
larity of this curve is very largely due to the very small number of 
records taken. 


a so 00** 


HALF 
■REVOLUTIONS 
OF 

DRUMS 


300 00 


zsooo 


20000 


13000 


/00003 


3000 


10 MILES 


9 



AGES 

1 

~ 21 DAYS 

X 

~ 10 0 ’’ 

<3 

~ 2/0 •> 

A* 

~ 270 •' 

cJ 

~ 4 SO » 

6> 

~ 60 0 ” 

ALL 

FEMALES 



1 




3 ? f 






































BEHAVIORISTIC STUDY OF THE RAT 


29 


This curve despite its irregularities has in general the same 
shape as the curves obtained by the other two methods. The 
age of maxiipum activity determined in this manner lies near 135 
days, which is about half way between 100 and 160 days, the 
ages of maximum activity determined by the other methods. 

Another aspect of this problem of the relation of activity to 
age was brought out incidentally in connection with the experi¬ 
ments on the revolving drums described above. 

It may be well to emphasize at this point that there is a tend¬ 
ency among workers interested in the activity of animals to 
confuse the activity of an animal due to external stimulation with 
the activity which manifests itself more or less spontaneously 
when the animal is free from all active external stimulation. 
Due to this confusion a number of workers say that the rat is most 
active at the age of thirty to forty days. They base this opinion 
very largely on the fact that every time they enter their labora¬ 
tories they find animals of this age active, while older animals 
remain inactive. They fail to take into consideration that the 
greater activity of the younger animals at these times may be due 
simply to the fact that these animals may be more sensitive to 
any external stimulation, noise made in entering the laboratory, 
and that during the rest of the time when they are not stimulated 
they may remain quite inactive. That is to say that younger 
animals are spontaneously less active than older animals, but 
that they are more sensitive to external stimulation. 

The differences between these two kinds of activity are brought 
out by the records of the activity of six animals of six different 
ages in the revolving drums. These drums both serve to stimu¬ 
late the animals and at the same time to record the activity in 
reaction to the stimulation. The stimulating effect of the drums 
is well known and can easily b£ demonstrated for every movement 
even the slightest destroys the equilibrium and causes counter 
compensatory movements to be elicited. How are animals of 
different ages affected by this stimulation? 

The records of this experiment are shown in figure 15 where the 
abscissae give the days of the experiment, while the ordinates 
give the total number of half revolutions made each day and their 


30 


CURT P. RICHTER 


equivalents in miles. The dotted ordinates indicate that no 
records were taken on the day preceding. 

It is seen that for the first day in the drums—none of these 
rats of course had ever been in the drums before,—the youngest 
rat 1 begins with by far the highest number of revolutions (7000) 
while the second and third youngest come next with 2500 revolu¬ 
tions, the fourth next with 1700, the fifth next with 1200, then 
the last with 30. This same relation holds for the rate of in¬ 
crease in the daily record for the first part of the experiment. 



Fig. 16. Curves Showing Schematically the Results of the Revolving 

Drum Experiment 

This daily increase as well as the general relation of the records 
of these animals is shown schematically in figure 16. 

Were the higher number of revolutions made by the younger 
rat due to greater activity then it should continue to make 
higher scores throughout the experiment. But it failed to do this. 
It was overtaken first by the 100 day rat and then by the 210 day 
rat. This same thing happened in turn to the 100 day rat. It 
is also finally overtaken by the 210-day animal. The higher 
number of revolutions at the beginnning of the experiment and 











BEHAVIORISTIC STUDY OF THE RAT 


31 


the more rapid increase and arrival at the maximum must have 
been due to the greater sensitivity of the younger animals to 
external stimulation. The very old animals were apparently 
not stimulated in the least by the drums. Their increase in 
activity from day to day was very gradual and seemed to depend 
almost entirely on the slow progressive adaptation and adjust¬ 
ment of the whole bodies to the drums. 

VI. PERSISTENCE OF RHYTHMS OF ACTIVITY AFTER WITHDRAWAL 

OF RHYTHMIC STIMULUS 

It may be well to add here a preliminary account of two experi¬ 
ments which help to throw further light on the general nature of 
spontaneous activity but from rather a different angle than in 
the previous experiments. Only a preliminary account is offered 
at this time because the experiments were carried out on just a 
few individuals and no opportuniy has presented itself for con¬ 
firming the results on larger groups. 

The first experiment was carried out in connection with the 
work described in Chapter II on the relation of spontaneous 
activity to starvation. In that work the interest was limited 
only to the changes in amount of activity during starvation. In 
the present experiment the interest was focused on the changes in 
the manner of expression of activity changes in the form of the 
activity distribution curve during starvation. It will be recalled 
that when the rat is kept in an environment of constant tempera¬ 
ture and illumination and fed just once per day at a definite time, 
the spontaneous activity is distributed in a regular way with 
relation to the time of the single daily meal. What happens to 
the shape of this curve when the factor upon which it depends 
is removed, that is when the animal is starved? 

Two animals were used for this experiment. They were kept 
in the laboratory under conditions of constant darkness and 
constant temperature for four months preceding the beginning 
of the experiment. During this time they were fed very regularly 
and punctually at a certain time just once per day. Care was 
taken to keep all of the conditions just as constant as possible 
throughout this entire period. 


32 


CURT P. RICHTER 


The records for the two animals are shown in figures 17 and 18. 
In these figures the time of the day is indicated on the abscissae, 
the amount of activity during each hour on the ordinates. A 
record of normal activity was taken on the day preceding the 
experiment, that is on the day before the animals were deprived 
of food. The record of the distribution of activity on this day 
is shown in the top curves marked ‘normal’. The shape of these 
curves corresponds in general outline to the composite distribution 
curve in figure 6. The records for the following days of starvation 
show that the general shape of this distribution curve is main¬ 
tained for three to four days after the removal of food. The 
curve becomes more and more flattened out with each day of 
starvation until on the fifth day it is practically a straight line. 

In the second experiment similar evidence was obtained. It 
was shown earlier that the rat is more active in the dark than in 
the light—and that progressively with age it becomes more and 
more active in the dark. The spontaneous activity then of 
animals that live in the open places where they are subjected 
to the daily changes of light and darkness of the day and night 
•will not be evenly distributed over the twenty-four hours, but 
will be confined for the greater part to the night hours. This will 
depend partly of course on the time the animals are fed. When 
however the food factor is eliminated by leaving the food in the 
cage all the time, then the activity should be limited even to a 
greater extent to the night hours. An animal in the open then 
is alternately active approximately for a period of twelve hours 
and then inactive for a period of twelve hours throughout its 
entire life. What happens to these alternating periods of activity 
and inactivity when the animals are placed in an environment 
of constant darkness? 

This was tried out in the following way. An animal was chosen 
for the experiment that was fairly old, 650 days, and which was 
still quite active,.and which also had been subjected to the daily 
change of light and darkness throughout its entire life. This 
animal was placed in the laboratory in complete darkness. There 
it was confined in a cage which was somewhat larger than the 
ordinary triangular cages. This cage had two small exits, one 



BEHAVIORISTIC STUDY OF THE RAT 


33 



after the removal of food 















34 


CURT P. RICHTER 













BEHAVIORISTIC STUDY OF THE RAT 


35 


leading into a revolving drum, the other into a 
food box in which food was left all the time. 
The animal could move freely from one cage to 
another as it chose. 

What then under these conditions happens to the 
periods of activity and inactivity set up through¬ 
out the 650 days of the animaFs life on the out¬ 
side? The results of this experiment are shown 
schematically in figure 19. In this figure only the 
activity in the drums is recorded. The first line 
gives the alternating periods of light and darkness 
in twelve hour periods 8:00 p.m. to 8:00 a.m. and 
8:00 a.m. to 8:00 p.m. for the 650 days of the 
animaFs life preceding the experiment. Also it 
shows the period of constant darkness during the 
experiment. The second line gives the probable 
relation of activity of the animal to the changes of 
light and darkness for the period of life before the 
experiment. It also gives schematically for twelve 
days the time relations of the revolutions of the 
drum made by the animal when placed in the 
environment of constant darkness. At the end of 
the twelve days the experiment had to be discon¬ 
tinued for unavoidable reasons. It may be seen 
that during these twelve days the regular daily 
alternation of activity and inactivity is fairly 
definitely maintained despite the constant dark¬ 
ness. How much longer this regular alternation 
of periods would have continued is difficult to 
conjecture. 

The fact of the persistence of rhythms of activity 
after the withdrawal of the rhythmic stimulus has 
been observed in a number of different animals in 
the past. Bohn and Keeble have interested them¬ 
selves very much with this phenomenon especially 
with relation to the life and habits of a small 
animal Convoluta roscoffensis which has its habitat 





























36 


CURT P. RICHTER 


on the foreshore of the sandy beaches of Normandy and 
Brittany. These workers found that the habits of this animal 
are to a very considerable extent dependent on the movements 
of the tide. Just before the tide reaches them at each flow 
they disappear into the sand, and just as soon as they are 
uncovered during the ebb they come up on the surface again. 
In this a very regular alternation of downward and upward 
movement is set up. Bohn (3) and Keeble (4) found further 
that when these animals are scooped up in a cup with some 
sand and placed in the laboratory where they are no longer 
subjected to the periodic coming and going of the tides they 
still continue for several days to make the upward and down¬ 
ward movements just the same. Benjamin Moore (5) has also 
described the persistence of a rhythm in absence of the wonted 
stimulus in the case of phosphorescent organisms in the sea. 
The organisms give off their light only at night. When they are 
placed in a dark room this daily alternation of phosphorescence 
and inactivity persists over a period of fourteen days after which 
time the animals usually die. 

VII. ON THE ORIGIN OF SPONTANEOUS ACTIVITY 

Throughout all of the experiments described thus far in this 
present study it was seen that a large part of the activity of the 
rat cannot be accounted for in terms of stimulation from outside 
sources. It was shown how some of the ever present factors, 
such as illumination and temperature may modify the expression 
of activity, but it was also shown that these factors could not be 
called upon to account for the activity. For this reason all that 
part of the activity of the rat that occurs in situations free from 
all external stimuli was spoken of as “ spontaneous ” activity. 
The source of this activity must lie somewhere within the organ¬ 
ism. What organ or mechanism is there within the body of the 
rat which might serve to bring about this gross bodily activity? .< 

In looking for this source of stimulation the chief characteristics 
of the manifestation of spontaneous activity studied above must 
be kept in mind; this is the very regular alternation of periods of 
activity and inactivity at the rate of ten to fourteen per twenty- 


BEHAVIORISTIC STUDY OF THE RAT 


37 


four hours. What mechanism is there within the body which 
functions in this way and at this rate? 

The heart and lungs although very regular and periodic in their 
functioning must be excluded for reason of their rate which is a 
matter of seconds and minutes rather than hours. The liver, 
rectum and bladder and intestines must be excluded for reason 
of their irregularity of periodicity. The sex glands, although 
periodic in their function, must be excluded because of their rate 
which is a matter of days, weeks or even longer intervals. 

There still remains the stomach. This organ has been the 
subject of very thorough investigation by a number of physiol¬ 
ogists, chiefly Cannon (6) and Carlson (7), so that its action is 
rather clearly understood. It has been established in the first 
place that the stomach when empty is not subject to continuous 
contractions as might be supposed, but rather that its activity is 
broken up into more or less clear-cut periods. During the 
intervals between the periods of activity this organ quite relaxed 
and almost completely inactive. During the activity periods it 
undergoes a series of contractions which may involve usually 
the greater part of the musculature of this organ. The rate of 
the recurrences of these periods differs in different species of 
animals, but also in members of the same species but of different 
ages. The average rate for most mammals when the stomach is 
empty is ten to fifteen per day. Under carefully controlled and 
regulated conditions these periods of activity may come with an 
astonishing regularity. 

These contractions of the stomach when this organ is empty 
must not be confused with the contractions that occur during the 
process of digestion when the stomach is full. These latter 
contractions are known as digestion contractions, while the 
former are known as hunger contractions. They differ in a num¬ 
ber of ways, first as to parts of the stomach involved, and secondly 
their relation in time to the last meal. The digestion contrac¬ 
tions begin almost immediately after an ordinary meal and con¬ 
tinue until the stomach is empty. Just as soon as any of the food 
is prepared for the assimilative processes in the alimentary canal 
below the stomach it is slowly expelled through the pylorus. The 


38 


CURT P. RICHTER 


process of expulsion involves the musculature from the sphyncter 
at the antrum to the sphyncter at the pylorus. Contractions 
begin at the antrum and work downward, one following another 
peristaltically. During the time the process of expulsion is going 
on the part of the stomach above the antrum is engaged in 
macerating and churning the food in acids preparatory to its 
descent below. These processes go on until the stomach is com¬ 
pletely emptied of food. As this process nears completion a new 
group of contractions begin, at first almost imperceptibly, gradu¬ 
ally increasing until finally the musculature of the entire 
stomach is involved. These are the so-called hunger contractions 
(see fig. 20). They occur only when the stomach is empty or 
nearly empty of food. These contractions begin at first at the 
lower end of the pylorus and work downward, each time however 
they begin farther and farther up on the wall of the stomach until 
they involve the entire fundus, and finally the entire stomach right 
up to the carclia. During these contractions marked changes 
take place in the entire organism, changes in blood pressure, 
intra-cranial pressure, reflex excitability, and in the heart-rate, 
while during the digestion contractions no such changes have 
been found to occur. The former contractions give rise to the 
sensations of hunger while the latter are not known to give rise 
to any kind of sensations. 

It is with these hunger contractions that this work will concern 
itself at this point. It was stated above that in the empty 
stomach they come in regular periods at the rate of ten to fourteen 
per twenty-four hours. This rate corresponds very closely with 
the rate of the spontaneous activity periods. The fact of this 
close correspondence in rate may be taken then to indicate 
that these two phenomena occur simultaneously or nearly 
simultaneously. 

Unfortunately it was not possible in the rat to get conclusive 
evidence of the simultaneity of the action of the stomach and the 
spontaneous gross bodily movments. Many attempts were made 
with the balloon method, but the difficulties of the technique due 
to the small size of the animals were too great. A number of 
animals were trained to take a very small stomach tube with a 


BEHAVIORISTIC STUDY OF THE RAT 


39 


balloon attached to the end, but in every case, some time before 
a record was taken, either the rat destroyed the tube by biting a 
hole through it, or else was destroyed itself by asphyxiation. 
The possibility of gastrostomy was considered-—that is making a 
small hole through the wall of the abdomen and introducing the 



Fig. 20. Hunger Contractions of the Dog’s Stomach Hours After a Meal 

A, Outline of bismuth coated balloon in stomach between the gastric contrac¬ 
tions; B, outline of balloon at the height of a hunger contraction (Rogers and 
Hardt) 


balloon into the stomach that way, but it was feared that the 
effects of the operation which are necessarily quite severe in such a 
small animal, because of the difficulty of handling such small 
parts, would too greatly modify the behavior to make the experi¬ 
ment practicable. 








40 


CURT P. RICHTER 


In humans however it has been possible to demonstrate this 
simultaneity of the contractions of the stomach and gross bodily 
movements. Miss Tomi Wada took simultaneous records on 
medical students of gross bodily movements and stomach con¬ 
tractions during sleep. The stomach contraction records were 
obtained by the usual method employed by Cannon and Carlson. 
The subjects swallowed the balloon and tube just before going to 
bed. The record of the gross bodily movements was obtained 
by means of a simple system of tambours placed under the bed. 
Records were taken during sleep because during the waking- 
periods the subjects are exposed to many external stimuli, and 
it is not possible to differentiate the part of the activity which is 
due to these external stimuli from the part that is spontaneous. 
Miss Wada found that the spontaneous movements during sleep, 
what few there are, rolling over in bed, etc. come periodically 
in regular groups. Miss Wada found further that in every 
case these periods of gross bodily activity coincided with the 
activity periods of the stomach. During the intervals between, 
when the stomach is quiescent, the body is also completely quiet. 
These results leave little doubt about the simultaneity of gross 
bodily movements and the activity of the stomach. 

Up to this point it has been shown that the stomach con¬ 
tractions and the periods of spontaneous bodily activity in all 
probability occur simultaneously. In any case of this kind where 
two phenomena occur simultaneously in this way the following 
possible explanations of the causal sequence may be made. (1) 
either both are due to some other common agent, (2) or else the 
bodily activity is the cause of the stomach activity (3) or finally 
that the stomach activity is the cause of the gross bodily activity. 

One of these explanations is easily eliminated; that the stomach 
activity is due to gross bodily activity. It is an experimental 
fact easily verified that contractions of the stomach cannot be 
elicited in anyway by activity of the whole body, rather on the 
contrary bodily activity tends to inhibit the contractions (Carlson 
and others). 

The second possibility that the stomach contractions and the 
activity have a common origin, a common stimulus may be elim- 


BEHAVIORISTIC STUDY OF THE RAT 


41 


mated by the following evidence. (1) It is a well-known fact 
that the stomach when completely excised from the body still 
continues to contract very much as before. This excised organ 
will continue to function for a considerable period of time if it is 
kept warm and moist and given the proper nourishment of oxygen. 
(2) Carlson and others have shown that the stomach functions 
quite normally in the body after complete nervous isolation from 
the rest of the body, after section of both vagi and both splancnics. 
Carlson sums up the evidence on this point in this way. . . . 
The essential point is that since the empty stomach, completely 
isolated from the central nervous system, does exhibit the typical 
hunger contractions, the primary role of the gastric nerves is 
that of modifying or regulating essentially automatic mechanisms 
in the stomach wall.” (3) The autonomous function of the 
stomach was further demonstrated by Carlson by means of a 
very ingenious experiment in which he used a Pavlov accessory 
pouch. In this experiment he found that “when the muscularis 
and myenteric isthmus joining the main and accessory stomachs is 
relatively narrow, the two stomachs exhibit complete independ¬ 
ence of the hunger contractions, even to the point of vigorous ac¬ 
tivity of the one during quiescence of the other.” 3 

There remains then the last of the three possibilities; that the 
spontaneous gross bodily activity is due to the activity of the 
stomach. This explanation seems to square best with the facts 
at hand at present on the activity of the stomach and the activity 
of the total organism. There are still so many gaps in our in¬ 
formation regarding both of the subjects that it is not possible 


3 Carlson regards the results of this experiment as very good evidence for the 
independence of the stomach from the stimulation of agents in the blood-stream. 
Carlson argues that the blood can have nothing to do with the stimulation since 
the stomach and the accessory pouch function independently though they are 
both supplied by the same blood. In interpreting these results in this way he 
does not give consideration to the fact of the local rhythms of the different parts 
of the stomach. It is well-known that strips of muscle taken from different parts 
of the walls of the stomach and placed in Ringer solution contract at quite dif¬ 
ferent rates. Every part has its own rhythm. In Carlson’s experiment then the 
possibility still remains that the main stomach and accessory pouch were stimu¬ 
lated by agents in the blood stream, but that because of their different inherent 
rhythms they responded independently. 


42 


CURT P. RICHTER 


at this time to be quite certain of any explanations of how the 
organism works. The investigations in recent years of Cannon 
and Carlson on the sensation of hunger and its relation to the 
stomach contractions have rather definitely established the fact 
that these contractions precede the hunger sensations in time, 
that they are the origin of these sensations. The results obtained 
in the present work seem to show that the stomach contractions 
do not alone bring about sensations of hunger, but they also 
bring about movements of the entire organism by means of which, 
as it will be shown in the following chapter, the organism is 
brought into contact with the materials necessary for stopping 
the contractions. 

A very important gap in our knowledge regarding the relation 
of the action of the viscera to the reactions of the whole organism 
was recently filled in by the work of Carlson and Luckhardt (8) 
on the visceral nervous system of frogs and turtles. In this work 
it was definitely established that stimulation of the visceral 
organs brings about reactions of the skeletal muscles, reactions 
of the whole organism. 1. “ Mechanical or electrical stimulation 
of the lungs, the gall bladder, the heart, the urinary bladder and 
the entire intestinal tract induces skeletal reflexes both in de¬ 
cerebrated and purely spinal preparations. 2. These visceral 
skeletal reflexes, at least as regards the extremities, are essentially 
of the defensive or escape type. ” 4 

The facts obtained in the present work on spontaneous activity 
and the facts known from physiological work on the stomach may 
tentatively be formulated in the following way: There is a 
tendency in all living organisms to maintain a metabolic balance 
or equilibrium. The various substances of the body are present 
in a fairly definite quantitative relationship. Whenever the 
balance is destroyed there is an immediate reaction to reestablish 
it. During fasting or during any time when the stomach is 
empty and the body is in need of nourishment this balance is 
temporarily destroyed. There is a minus of some substances and 

4 We found recently in a series of experiments on the behavior of foetuses (cats) 
still attached to the cord that stimulation of the stomach or intestine (slight 
pinching) elicits very vigorous movements of the entire body. 


BEHAVIORISTIC STUDY OF THE RAT 


43 


a plus of others. The products of this deficiency—whatever they 
are—may be looked upon as the agents which set up the process 
of reestablishing the equilibrium. (This process has for its final 
step the movements of the entire organism about in the environ¬ 
ment until contact with food is made and the food is ingested.) 
As far as is known there is no way for these deficiency products, 
which are probably carried in the blood stream, to stimulate the 
skeletal muscles directly—the muscles which bring about the 
movements of the entire organism. How then is the equilibrium 
reestablished? It is known from direct work on the stomach and 
from analogous work on the heart that the stomach responds to 
chemical stimulation, that its activity may be influenced and 
changed by chemical stimulation. It is safe to assume that these 
deficiency products stimulate the stomach, bring about in it an 
increase in size and rate of the contractions. These contractions 
in turn when they become large enough send impulses to the 
skeletal muscles through the vagi and central nervous system, 
efferent nerves, and release there the stored energy which 
starts the organism in operation of getting food for filling the 
stomach. The fact then that the energy in the muscles is only 
released periodically as was demonstrated above must be ac¬ 
counted for by the periodicity of the action of the stomach. This 
organ is subjected during times when the body is in need of 
nourishment to a continuous stimulation from the deficiency 
stimuli. Progressively as the strength of the stimuli increases 
more and more of the stomach wall responds until the entire 
organ from the cardia to the pylorus becomes involved. After 
a long series of contractions of this kind the musculature finally 
reaches a condition in which suddenly the deficiency stimuli 
are no longer able to elicit a reaction, the contractions cease and 
the stomach becomes quiescent. This quiescent phase which 
follows may be thought of as a period of fatigue in which for the 
time being the muscles are temporarily no longer responsive to 
stimulation. As the muscles recuperate the contractions begin 
again, and progressively as the recuperation process goes on 
they become larger and larger until finally the height of another 
period is reached and the entire reaction is repeated. This 




44 


CURT P. RICHTER 


accounts for the periodicity of the action of the stomach and at 
the same time for the periodicity of the spontaneous gross bodily 
activity of the whole organism. 

Schematically this tentative formulation may be expressed in 
the following manner. Before presenting this schema, however, 
it is necessary to recall in this place several points brought out 
above in Chapter I in the experiments which deal with the 
periodic nature of spontaneous activity, when the animals were 
kept in a small cage and fed just once per day. In these experi¬ 
ments it was found that the spontaneous activity comes in regular 
periods which are separated by intervals of almost complete 
quiescence and that the activity is not evenly distributed through¬ 
out each period. There is only very slight activity at first. 
Progressively as the period goes on the activity increases until 
a maximum is reached either in the middle or toward the end of 
the period. It must also be recalled here that the stomach 
contractions are not all of the same size. Each of the contraction 
periods begins with very small contractions which involve only 
a limited part of the stomach. The contractions become larger 
and larger until the entire stomach is involved from the cardia 
to the pylorus. This maximum of activity is usually maintained 
right up to the end of each period. Following the cessation of 
the contractions the stomach becomes completely quiescent. 
The relation of spontaneous activity to the function of the stomach 
is shown schematically in figure 21. In this figure spontaneous 
activity is given on the top line while the probable relation of the 
stomach contractions to this activity is given on the second line. 
In this schema it is intended to show that the gross bodily activity 
of the organism increases progressively as the activity of the 
stomach increases. The maximum of spontaneous activity is 
reached when the whole stomach becomes involved in the con¬ 
tractions. With the cessation of the contractions of the stomach 
at the end of each period the animal becomes inactive. This 
process repeats itself with each new period of stomach contrac¬ 
tions. This relation will be discussed in more detail in the 
following chapter. 


BEHAVIORISTIC STUDY OF THE RAT 


45 


It must be emphasized that with this 
tentative formulation it is not intended to 
imply that the stomach is the only organ in 
the body upon which spontaneous activity 
may depend. But it is true however that a 
larger part of the activity of the rat does 
fall into these regular clear-cut periods, which 
have been associated with the action of the 
stomach. Besides this activity which falls 
into the regular periods there still remains 
some activity which the limited scope of the 
present work did not permit to be studied 
in detail. Most important here is a rather 
considerable amount of irregular activity of 
females. Whether this irregular activity is 
related to the action of any part of the sexual 
apparatus was not determined. The role 
that the stomach mechanism plays with 
relation to spontaneous activity probably 
varies very greatly in the different species 
of animals. In the lower organisms it must 
undoubtedly account for a very much larger 
part if not all of the spontaneous activity. In 
man, on the other hand, it probably accounts 
for only a limited part of the activity. Still 
the work described above on the relation of 
spontaneous activity to the stomach con¬ 
tractions in humans during sleep would 
indicate that the stomach still plays a very 
important role in bringing about activity 
even in humans, however greatly covered 
over this activity seems to be by the flood 
of reactions elicited by the many different 
external stimuli during waking periods. In 
this connection it would be of importance 
to determine the relation of spontaneous 
activity to the kind and structure of the 



o 

M 


. 21 . Relation of Stomach Contractions to Activity 





















46 


CURT P. RICHTER 


stomach. In frogs for instance the stomach happens to be 
so constructed that it is able to adapt itself to very large 
quantities of food. This animal gets its food only at rather 
great intervals—weeks or months—but then usually in a single 
large quantity, other smaller frogs or the like, which take many 
days to be digested. What is the relation between this kind of 
a stomach and the spontaneous activity of the animals? The 
human stomach on the other hand is so constructed that it is 
able to take only relatively small quantities of food at one time, 
but this food is digested almost immediately. A study also of 
the relation of activity to the action of the stomach should be 
very interesting in ruminants where the stomach is made up of 
several separate parts. What does the animal do spontaneously 
during the function of each of these parts? 

There is still another point which argues very strongly for the 
prime importance of the stomach with relation to the other in¬ 
ternal organs especially the bladder and rectum, in bringing about 
about activity. This is the fact that in all animals, and in man 
living in the wilds, distention of the bladder and the rectum is 
relieved wherever the individual happens to be while the con¬ 
tractions of the stomach can only be relieved by movements of 
the organism about in the environment until contact with food is 
actually made and the food is ingested. 

In light of this explanation some of the results obtained in 
earlier chapters especially from the work on the distribution curve 
of activity may now be discussed again. It will be recalled that in 
these experiments it was shown that when the animal is fed just 
once per day and under conditions of constant illumination and 
temperature the spontaneous activity is distributed over the 
twenty-four hours in a very definite way (see figure 6). The form 
of the activity distribution curve was shown to depend on the time 
of the last feeding. The two phases of inactivity and the single 
period of intense activity shown in this curve may be explained 
on the basis of the formulation given above in the following way. 
The first period of inactivity immediately after the daily meal 
occurs at a time when the processes of digestion are going on in 
the stomach and when the hunger contractions are absent. After 
the stomach empties the hunger contractions begin again and 


BEHAVIORISTIC STUDY OF THE RAT 


47 


become more and more vigorous with each succeeding period. 
The animal is stimulated in this way only slightly at first but in¬ 
creasingly more intensely until it reaches its maximum of activity 
some twelve hours after the daily meal. At this time the nervous 
system and the large muscles of the body employed in making the 
spontaneous movements become fatigued so that although the 
stimulation from the stomach still continues in its periodic 
fashion these muscles respond only with a very small amount of 
activity. During this period of fatigue the attempts of the 
stomach to gain control of the organism, to start it to activity 
are clearly manifested by the small but regular periods of activity 
shown at this time. This may be looked upon as the period of 
sleep. Actual observation showed that during this period the 
animals are very difficult to arouse they are curled up in balls 
and are as far as can be made out “ sleeping. ” It has already 
been pointed out in Miss Wada’s work on the activity of humans 
that during sleep the period of activity and inactivity come and 
go with great regularity synchronous with the stomach contrac¬ 
tion periods. The stomach continues to function during this 
period of sleep just as vigorously as before. The amount of 
activity becomes larger and larger with each successive period 
until finally, after a condition of sufficient recuperation of the 
nervous system and skeletal muscles is reached, the stomach 
contractions again gain possession of the reactions of the whole 
organism and the individual awakes. The regular anticipation 
of the feeding periods may also be explained on the basis of the 
clock-like functioning of this internal organ. When all external 
conditions are kept fairly constant and when a regular routine of 
activity is gone through each day the accuracy of this time piece 
is quite astonishing. This is seen very well in the activity record 
of individual rats, but it is much better known from numerous 
observations from the great regularity and punctuality of the 
reactions of many farm animals, especially of the braying of the 
mule at a very definite time near noon at which it is accustomed 
to be fed. The ability to carry on other rhythms may be ex¬ 
plained on this basis (9 and 10). 5 

5 A good example of the persistence of a rhythm of activity of an internal organ 
after the removal of the original exciting stimulus is found in the case of the 


48 


CURT P. RICHTER 


VIII. RELATION OF SPONTANEOUS ACTIVITY TO HUNGER 

The intimate relation of gross bodily activity and the 
action of the stomach was pointed out in the previous chapter. 
There still remains the question as to the relation of this gross 
bodily activity to the hunger reactions of the animal. Does it 
follow that because this diffuse form of activity is due to the 
stimulation from the stomach that it must all necessarily be 
translated into hunger reactions, searching for food, eating, etc.? 
It was shown that each of the regularly recurring periods of gross 
bodily activity is connected with simultaneous periods of activity 
of the stomach. Is all of the activity in each of these periods 
hunger activity? 

In order to answer these questions and a number of allied ques¬ 
tions a simple construction was used, the ‘double cage.’ This 
arrangement consists of an ordinary triangular activity cage with 
a hole cut in one side large enough to permit of the easy introduc¬ 
tion, without contact, of the snout of an inverted pipe-shaped 
smaller tube containing food. Both cages were supported on a 
separate set of tambours and the activity in each cage was regis¬ 
tered separately. A photograph of the double cage is shown in 
figure 22. The small round cage contains a metal food receptacle 
which is so constructed that the food may be easily gotten at 
through the hole at the top large enough to accommodate the 
head of the rat, but too small to permit the rat to pick up food in 
its paws and to scatter it about or possibly even to take some of it 
back into the other cage. In this experiment food was left in 
the food receptacle all the time, and water was left in the water- 
glass attached to the outside of the triangular cage. Of course, 
there is an obvious possibility of the animal's entering the food 
box for other purposes than replenishing itself with food. In 
order to eliminate this possibility the food cage was made just 

human uterus. This organ, especially in multiparous women, continues to con¬ 
tract for a number of days after the birth of the child. The contractions are 
originally set up by the presence of the foetus. All during pregnancy these con¬ 
tractions go on. But interestingly in this connection they are not felt until 
labor begins, when they serve to expel the foetus. After labor they still continue 
to be felt for a number of days (that is they are still strong enough to dominate the 
organism). 


BEHAVIORISTIC STUDY OF THE RAT 


49 


large enough to permit the rat to enter and to get at the food, 
but too small to permit of very much sniffing or moving about. 
This arrangement was quite successful. It was possible to 
veiify this by actual observation over rather long periods of time, 







mmiBm 

1,5>' • ,»- T* 


'•r'*’*'** 

-?•». £ y * ? 


■iRaMii • 


■ •- 

«; »*• 

5**« 


•» -Hit* • • * •’•ma<a£ £•*»• 


’SSKfl&i 

:sg|!|i{! 




^ - ■ 






: 


■: - 


Fig. 22. Photograph of Double Cage 


after the animals had had a good chance to accommodate them¬ 
selves to the particular form of cage. After the first day in the 
double cage, they rarely, if ever, entered the food box when just 
generally active and sniffing about. When they did enter they 
seemed to do so solely for the purpose of getting food. 


50 


CURT P. RICHTER 



The results obtained from this experi¬ 
ment (see figure 23) showed: (1) In this 
situation where the animals had free 
access to food all the time the periods 
of activity and inactivity come and go 
with the same regularity as before only 
at a slower rate from six to ten per 
twenty-four hours. (2) The animals 
enter the food box at least once during 
each activity period, occasionally twice. 
(3) The time spent in the food box 
compared with the length of the entire 
period is very short. (4) The entrance 
into the food box does not take place at 
the beginning of the activity period but 
usually toward the end. Only in a few 
cases did any of the animals enter the 
food box at the beginning of a period. 
No instance of an entrance between 
periods was recorded. (5) The amount 
of activity increases progressively from 
the beginning of each period to the point 
when the animal enters the food box. 
(6) There is always some activity after 
the animal returns from the food box. 
This activity consists chiefly in all kinds 
of cleansing manoeuvers very much like 
those of an ordinary house cat. (7) The 
activity which precedes the entrance into 
the food box is diffuse and undirected. 
It consists usually of such movements as 
jumping, climbing, playing with paper, 
sniffing and gnawing at the sides of the 
cage, etc. The element of search for 
food plays no role in this activity. The 
animals are so thoroughly adjusted to 
every part of the cage that the necessity 
of search drops out entirely. 







BEHAVIORISTIC STUDY OF THE RAT 


51 


In order to bring these results into relation with the activity 
of the stomach it is necessary to bring out some additional facts 
regarding the function of the stomach. (1) Each period of 
activity of the stomach begins with small contractions. These 
contractions come with a very regular rate, one every eighteen to 
twenty seconds. For the reason of this rate Carlson speaks of 
these contractions as the “ twenty-second rhythm. ” These 
contractions become larger and larger as the period advances 
without changing their rate. (2) After these contractions have 
reached a certain size, quite abruptly a new series of very 
much larger contractions beings. These larger contractions come 
at a different and irregular rate, and also have a different form. 
These are the so-called “ main hunger contractions. ” Whether 
or not there is any real difference between the small and the large 



Fig. 24. Relation of Stomach Contractions to Activity in Double Cage 


contractions besides what can be explained in terms of the 
different extent to which the musculature of the stomach is in¬ 
volved in the two cases is not definitely known. (3) Cannon 
was the first to show that these large contractions give rise to the 
sensation of hunger and (4) Carlson has shown that the intensity 
of the hunger sensation is roughly proportional to the size of 
the contraction. 

The relation of the results obtained in the 1 double cage’ to 
these facts is brought out in figure 24. In this figure the diffuse 
spontaneous activity in the double cage is shown on the top 
line. The entrances into the food box are shown on the second 
line. The probable relation of the stomach contractions to the 
diffuse activity and to the entrances into the food box is shown 
on the bottom line. The small contractions serve only to stimu¬ 
late the animal to diffuse activity, restlessness. It is not until 






















52 


CURT P. RICHTER 


the onset of the large contractions, the main hunger contractions, 
that the animal enters the food box. With the introduction of 
food into the stomach the contractions cease. Once started at 
eating, however, the animal continues until the stomach is filled. 
The activity in the cage following the return from the food box 
is made up entirely of cleansing manoeuvres elicited by the 
various kinds of external stimulation connected with eating. 

The fact that the animal does not enter the food box until the 
onset of the large contractions may be explained in the following 
way: At birth the members of all mammalian species are known 
to have contractions of the stomach almost continuously 
(Carlson). Driven then by these contractions the animals are 
active diffusely and remain active until either stomach contrac¬ 
tions are in some way stopped, or else due to gross exhaustion 
the animals are no longer able to move. They move and toss 
their heads about here and there, suck at everything that happens 
to stimulate their lips, bits of straw, hair of the mother’s body, 
feet and ears of sisters and brothers, and finally the teats of the 
mother. It is only the last of these activities that brings about 
a change within the organism. When the teats touch the lips 
sucking movements are elicited; a warm stream of milk flows 
down the animal’s throat; the stomach contractions are stopped; 
hunger pangs are relieved; the animal lies down and goes to 
sleep. Each time the contraction periods begin again the animal 
becomes active; begins moving about and sucking at everything 
and the whole process is repeated. As this trial and error proc¬ 
ess goes on, the onset of the stomach contractions gradually 
becomes more and more definitely associated with the sucking 
of the teats, becomes the main motor outlet, while the others 
fall into disuse. This process goes on for a time; in the rat it is 
a matter of days (as near as I could determine by observation, 
eight or ten days); in the human infant it is a matter of months 
until the stomach contractions elicit the one reaction of crying 
and actually seeking food. This process is somewhat complicated 
by the fact that the stimulus to activity is not at all times the 
same, for, as was shown above, the stomach contractions vary 
considerably in amplitude, also possibly even in their nature 


BEHAVIORISTIC STUDY OF THE RAT 


53 


during different parts of the contraction period. If the animal 
happens to find the teats during the part of its activity which is 
caused by the milder contractions it will nurse just as at any 
other time; but the changes that take place within the organism 
when milk or food is taken during this part of the contraction 
period are so slight that no definite associations can be built up 
between them and the sucking at the teats and the taking of 
food. When however, the animal happens to find the teats 
during the period of main stomach contractions things are quite 
different. Now the changes resulting from the taking of the milk 
are strong enough to become associated with the stomach activity, 
and form the basis of the cycle: stomach contractions—going- 
out to teats—nursing—inhibition of contractions—relief. There 
are further reasons why these reactions become associated more 
readily during the period of strong contraction: first the fact that 
during the period of strong contractions the animals are more ac¬ 
tive and vigorous than during the period of milder contractions; 
secondly chances and the frequency on a simple trial and error 
basis of finding the teats during the former period will be much 
greater. Then also for the reason that milder contractions are 
more easily stopped the animal will nurse for a shorter time during 
this part of the period. Besides these simple factors of frequency, 
duration, recency of stimulation, there will be other rather more 
situational factors which will help to build up the association; 
such things as odor of the teats, the warmth of the mother’s 
body, etc., and, of course, the encouraging reaction of the mother 
herself. 

Gradually the main stomach contractions and the sucking of 
the teats become permanently associated and there is less tend¬ 
ency for the animal to suck at the teats during the period of weaker 
contractions. The onset of the main stomach contractions comes 
to serve as a signal for the taking of food and the animal no longer 
hesitates but goes directly to the teats. Later on, after the 
animals are weaned, as was the case in the double cage, the onset 
of the main contractions served as a signal for the animal to go 
to the food box. 


54 


CURT P. RICHTER 


It is hoped that further light may be thrown on the origin of 
these specific food reactions by work that is now being carried on 
by Mr. Ging Wang on the activity of the newly born of rats and 
cats before they have ever been fed. Mr. Wang is attempting to 
find out when the periodicity begins, whether or not it is present 
at birth, and what relation it has to the times of feeding, and the 
time required for the complete emptying of the stomach. He 
also hopes to get some information on these reactions during the 
period of the animal’s life before it is born. It is astonishing how 
little definite information is available at present regarding the 
activities during this very important time of development. 

The facts on hand from work on the activity of the human in¬ 
fant present certain difficulties which are not easily explained. 
Miss Wada found in her work that the gross bodily movements of 
the infant during sleep come in periods at the rate of one every 
fifty-five minutes. It is difficult to see how this rhythm could 
have been set up by any external stimuli in as much as the infant 
on which these records were taken was fed once every four hours 
from birth on. In adults the periods of activity come at the rate 
of one every two hours. But in adults we have shown definitely 
that these periods occur simultaneously with the periods of ac¬ 
tivity of the stomach. Here again, however, the relation of the 
food habits to the periods of activity is difficult to explain. 
The solution of these problems must wait for further evidence. 

REFERENCES 

(1) Szymanski, J. S.: Versuche ueber Aktivitaet und Ruhe bei Saeuglingen. 

Pfluegers Archiv, 1918, clxxii, p. 424. 

Szymanski, J. S.: Die Verteilung der Ruhe und Aktivitaetsperioden bei 
einigen Tierarten. Pfluegers Archiv, 1918, clxxii p. 430. 

Szymanski, J. S. : Aktititaet und Ruhe bei Tieren und Menschen. Zeit. f. 
Allgemeine Physiologie, 1920, xviii, p. 105. 

(2) Slonaker, J. R.: The normal activity of the white rat at different ages. 

J. Comp. Neur. and Psychol., 1907, xvii, pp. 342-359. 

Slonaker, J. R.: The normal activity of the albino rat from birth to natural 
death, its rate of growth and the duration of life. J. Animal Behav¬ 
iour, 1912, ii, pp. 20-42. 

(3) Bohn, G.: Sur les movements oscillatoires des convoluta roscoffensis. 

C. R. Ac. Sc., Oct., 1903. 

(4) Keeble, Frederick: Plant-Animals, Cambridge Manuals of Science and 

Literature, Cambridge, 1910. 


BEHAVIORISTIC STUDY OF THE RAT 


55 


(5) Moore, Benjamin: Origin and Nature of Life. Home University Library. 

(6) Cannon, W. B.: The Mechanical Factors of Digestion, New York, 1911. 
Cannon, W. B.: Bodily Changes in Pain, Hunger, Fear and Rage. New 

York, 1920. 

(7) Carlson, A. J.: The Control of Hunger in Health and Disease. The Univer¬ 

sity of Chicago Press, Chicago, 1916. 

(8) Carlson, A. J., and Luckhardt, A. B.: Studies on the sensory nervous 

system. VII. Skeletal reflexes induced by stimulation of visceral 
afferent nerves in the frog and turtle. Am. Jour, of Physiol., 1921, 
lv, p. 366. 

(9) Froehlich, Fried. W.: Ueber die rhythmische Natur der Lebensvorgaenge. 

Zeit. f. Allg. Physiologie, 1912, xiii. 

(10) Boldyreff, W.: Function periodique de Porganisme chez l’homme et les 

animaux d’ordre superieur. Quart. Jour, of Exper. Physiol., 1916, x, 
p. 175. 

(11) Wada, Tomi: An experimental study of hunger in its relation to activity. 

Arch, of Psych., 1922, lvii. 




Directory of American Psychological Periodicals 


American Journal of Psychology—Ithaca, N. Y.: Morrill Hall, 

Subscription $6.50. 600 pages annually. Edited by E. B. Titchener. 
Quarterly. General and experimental psychology. Founded 1887. 

Pedagogical Seminary—Worcester, Mass.: 950 Main Street. 

Subscription $5. 575 pages annually. Edited by G. Stanley Hall. 

Quarterly. Pedagogy and educational psychology. Founded 1891. 

Psychological Review—Princeton, N. J.: Psychological Review Company. 
Subscription $4.25. 480 pages annually. 

Bi-monthly. General. Founded 1894. Edited by Howard C. Warren. 

Psychological Bulletin—Princeton, N. J.: Psychological Review Company. 
Subscription $5. 720 pages annually. Psychological literature. 

Monthly. Founded 1904. Edited by Shepherd I. Franz. 

Psychological Monographs—Princeton, N. J.: Psychological Review Company. 
Subscription $5.50 per vol. 500 pages. Founded 1895. Ed. by James R. Angell. 
Published without fixed dates, each issue one or more researches. 

Psychological Index—Princeton, N. J.: Psychological Review Company. 
Subscription $1.50. 200 pages. Founded 1895. Edited by Madison Bentley. 
An annual bibliography of psychological literature. 

Journal of Philosophy—New York: Sub-station 84. 

Subscription $4. 728 pages per volume. Founded 1904. 

Bi-weekly. Edited by F. J. E. Woodbridge and Wendell T. Bush. 

Archives of Psychology—Sub-station 84, New York: Archives of Psychology. 
Subscription $5. 500pp. per vol. Foundedl906. Edited by R. S. Woodworth. 
Published without fixed dates, each number a single experimental study. 

Journal of Abnormal Psychology and Social Psychology—Boston: 
Subscription $5. Richard G. Badger. Edited by Morton Prince. 

Bi-monthly. 432 pages annually. Founded 1906. Abnormal and Social. 

Psychological Clinic—Philadelphia: Psychological Clinic Press. 

Subscription $2.50. 288 pages. Edited by Lightner Witmer. Founded 1907. 
Without fixed dates (9 numbers). Orthogenics, psychology, hygiene. 

Journal of Educational Psychology—Baltimore: Warwick & York. 
Subscription $4. 540 pages annually. Founded 1910. 

Monthly (9 numbers). Managing Editor, J. Carleton Bell. 

(Educational Psychology Monographs. Edited by Guy M. Whipple. 

Published separately at varying prices. Same publishers.) 

Comparative Psychology Monographs—Baltimore: Williams & Wilkins Co. 
Subscription $5. 400 pages per volume. Edited by W. S. Hunter. 

Published without fixed dates, each number gives one or more researches. 

Psychoanalytic Review—Washington, D. C.: 3617 Tenth St., N. W. 
Subscription $6. 500 pages annually. Psychoanalysis. 

Quarterly. Founded 1913. Ed. by W. A. White and S. E. Jelliffe. 

Journal of Experimental Psychology—Princeton, N. J.: 

Psychological Review Company. 480 pages annually. Experimental. 
Subscription $4.25. Founded 1916. Bi-monthly. Edited by John B. Watson. 

Journal of Applied Psychology—Worcester, Mass.: Florence Chandler. 
Subscription $4. 400 pages annually. Founded 1917. 

Quarterly. Edited by James P. Porter and William F. Book. 

Journal of Comparative Psychology—Baltimore:Williams & Wilkins Company. 
Subscription $5. 500 pages (annually). Founded 1921. Bi-monthly. Edited by 
Knight Dunlap and Robert M. Yerkes. 

Journal of Personnel Research—Baltimore: Williams & Wilkins Company. 
Subscription$5. 500pages (annually). Founded 1922. Monthly. Edited by 
Leonard Outhwaite. 


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